WO2001066213A1 - Liquid distributor and method for operating the same - Google Patents

Abstract

The invention relates to a liquid distributor for packed and/or filled columns, comprising individual, in particular horizontal layers involved in heat and/or material exchange. At least one layer of the column has a flooding, in particular for obtaining an increased density and for creating an accumulation of liquid and a specific surface for distributing the liquid. Said surface is greater than the surface of the overlying and underlying layers by a factor of 1.5 to 10, preferably by a factor of 2 to 3.

Description

Liquid distributor and method of operation

The invention relates to a liquid distributor for packed and / or packed columns with individual, in particular horizontal, layers involved in the heat and / or mass transfer.

In distillations, absorptions, gas washes and similar process operations, columns are used that contain internals for the heat and mass transfer between liquid and gas. These internals either consist of floors, such as bell floors, tunnel floors, dual flow floors, sieve floors or valve floors, of randomly arranged packing elements, such as Raschig rings, pale rings or saddle bodies, or of orderly packings. In the ordered packings, geometries in a cross-channel structure have become widely used in technical applications. Standard designs are, for example, the types Montz A3, BSH and B1 from Montz GmbH, D-40705 Hilden, the types Sulzer BX, CY and Mellapak from Sulzer Chemtech AG, CH-8404 Winterthur, the type FLEXIPAC from Koch -Glitsch, Wichita, Kansas 67208 (USA) and the Intalox type from Norton, Akron, Ohio 44309 (USA).

In the case of packed columns and packing columns, there is a need to set a distribution of liquid and gas that is as uniform as possible over the column cross section in order to achieve a high separation performance. The uniform distribution of the gas is easy to implement, since the inevitable pressure loss of the packing and packings automatically results in a largely uniform distribution of the Gas flow across the column cross section causes that is sufficient for most technical applications.

The problem of even distribution of liquid over the reactor cross section also arises with fixed bed reactors in order to avoid the occurrence of local overheating, so-called hot spots. It has therefore proven to be advantageous to use distribution devices for the liquid.

The uniform distribution of liquid across the column cross section is difficult to achieve. Special distributors for the liquid are required. A large number of distributor constructions are used in the art, which work on the principle of the accumulation of liquid, the free overflow or the atomization. In K. Sattler: "Thermal separation process" (1988), VCH Verlagsgesellschaft mbH, D-69451 Weinheim, pages 226 to 231 provide an overview of technically common distributor constructions.

The simplest form of liquid distributors are edge deflectors, as are described in US 3,099,697, which discharge the liquid from the column wall and give it up again at some distance from the column wall. An equalization of the liquid sprinkling density in the remaining area of the column cross section is not brought about.

In some cases, nozzles are used to distribute the liquid across the column cross-section. However, the distribution quality that can be achieved is limited, so that this distribution principle can only be found in simple applications, such as absorption or gas scrubbing.

Distributors are more widespread, in which the liquid to be distributed runs out of containers which are open at the top, mostly branched channels and which extend over the column cross section, via overflow devices. These overflow devices consist, for example, of serrated weirs and have to be aligned exactly horizontally in order to ensure a uniform liquid distribution over the column cross-section. Likewise, pipes with openings at the bottom can be distributed in a cross-section Pipe system to give up the liquid to be distributed. Here, too, the pipes must be aligned as horizontally as possible.

Since this precise horizontal alignment is difficult to achieve with the required accuracy in practice, distribution systems that work on the accumulation principle are used in applications with high demands on the distribution quality. Here the liquid does not run out of the channels via overflow weirs, but through narrow openings in the lower area of the channels. Since the liquid accumulation height in the operating state is generally about 0.05 to 0.15 m, inaccuracies in the horizontal alignment of the distributor device do not have the same effect as in distributor systems which operate on the overflow principle. However, the manufacturing effort is considerably higher. Examples of this type of construction are EP 374 443 B1, EP 462 048 B1, EP 462 049 B1, EP 434 510 B1, DE 19 615 645 A1, US 4,476,069, US 5,501,079, US 5,192,465, and US 5,518. 667th

For very high demands on the distribution quality, special constructions are used which, in addition to the accumulation of liquid, also use the capillary distribution effect. Examples are described in EP 512 277 B1 and US 4,432,913.

Another principle for achieving a high distribution quality is the intermittent application of individual distribution points for the liquid. An example can be found in US 4,776,989.

US 4,569,364 describes a distributor which can be specifically adjusted from the outside.

US 5,776,316 describes a collecting and distributing device which additionally enables liquid to be exchanged in a targeted manner across the column cross section.

US Pat. No. 5,387,377 describes a structurally complex device in which an attempt is made to also use the distribution device as a mass transfer element to use. The parts of the device through which gas flows contain packings which support the mass transfer and are matched to the other mass transfer elements in the gas throughput.

A similar effect is sought in US 5,695,548. A total of distribution channels, which are arranged one above the other in several layers, are flowed through by gas and liquid in cocurrent. This improves the exchange of substances.

Distributors must be provided in packed columns and packing columns at the top of the column for distributing the reflux liquid and at all feed points for liquid feeds. In addition, in the case of larger column numbers, it is customary to make intermediate distributions for the liquid. These intermediate distributions suppress the adverse effects of liquid maldistributions, such as marginalization or creek formation.

The need for liquid distributors represents a considerable economic impairment when using packed columns and packing columns. In particular, the redistribution of liquid in column 1 is complex, since the liquid flowing out of the mass transfer packs 6 and to be redistributed is first collected in a liquid collector 2 via a Collecting channel 3 and a discharge pipe 4 are guided and fed to the liquid distributor 5 (Fig. 1). The minimum overall height for the overall arrangement of the collector, collecting trough, discharge pipe and distributor is also around 1 m for small column diameters, and 1.5 to 2 m for large column diameters. Since several of these devices are required in one column, this leads to column heights which are increased by about 25% and higher investment costs.

In the case of liquid mixtures with phase disintegration in the liquid phase, this is aggravated by the fact that the usual distributor constructions are difficult to ensure the uniform distribution of the two liquid phases over the column cross section. In the case of phase decay, you are usually forced to do both First separate liquids in a phase separation vessel and then pass them over two separate distribution systems.

The object of the invention is to obtain an optimal distribution and redistribution in a structurally simple manner, in particular without additional redistribution station and with a low overall height.

According to the invention, this object is achieved in that at least one layer of the column has a greater density and thus for flooding, in particular flooding and for a distribution of the liquid, a specific surface which is by a factor of 1.5 to 10, preferably by a factor of 2 to 3 is larger than the surface of the layer above and below.

The present invention provides a simple device with which the effort for the distribution and in particular the redistribution of liquid is greatly reduced. It is suitable for packed columns and packing columns, but especially for use in packing columns. Surprisingly, this distribution effect can be achieved without the need for additional assemblies, such as liquid collectors, collecting channels, drain pipes and distribution systems. The liquid-distributing effect is achieved by a modification and / or addition of the internals effecting the mass transfer according to the invention. The areas of the column which effect the liquid distribution also take part in the mass transfer. This reduces the height of the column. This new type of distributor also allows the distribution of two-phase liquid mixtures without the occurrence of phase decay.

Advantageous embodiments of the invention are listed in the subclaims.

Embodiments of the invention are shown in the drawings in mostly vertical sections and are described in more detail below. Show it 1 shows a redistribution according to the prior art,

2 shows an embodiment according to the invention with a distributor layer, in particular a distributor packing layer,

Fig. 3 is a perspective section of a pack with a cross-channel structure,

Fig. 4 Form and assembly of individual sheets,

Fig. 5 single sheets with kink gradients,

Fig. 6 a version with support ring and support grate,

Fig. 7 Distribution packs / layers with increased flow resistance and

Fig. 8 two distributor packs / layers arranged directly one above the other.

It has been found that the liquid-distributing effect can be brought about by thin, approximately 1 to 20 cm, in particular 2 to 4 cm high packing layer layers 7 - hereinafter referred to as distributor packing 7 - or layers of packing elements - hereinafter referred to as distributor layer 8 - which have a larger volume-related surface and a smaller hydraulic diameter than the other packs 6 or filler 9 (Fig. 2). The distributor packs preferably have perforations in the form of, for example, circular holes, the proportion of the perforations in the total area being about 2 to 80%, preferably 10 to 30%. It is also possible to achieve the effect of the perforations by using, for example, expanded metal as the starting material, as is customary on the market for packs of the Montz BSH type. The volume-specific surface area of the packing layers is greater than that of the distillation packs by a factor of approximately 1.5 to 10, preferably by a factor of approximately 2 to 3. The geometry of these distributor packs is arbitrary. In principle, the geometries customary in distillation packs can be used, for example the particularly widespread cross-channel structures. Figure 3 shows a section of such a package with a cross-channel structure. This geometry is particularly advantageous since, even with a high proportion of perforations, as is preferred for the distributor packs 7, it still has a high mechanical strength, in particular pressure resistance. Examples of suitable packing geometries are the types Montz A3 and B1 from Montz GmbH, D-40705 Hilden, the types Sulzer BX, CY and Mellapak from Sulzer Chemtech AG, CH-8404 Winterthur, the type FLEXIPAC from Koch- Glitsch, Wichita, Kansas 67208 (USA) and the Intalox design from Norton, Akron, Ohio 44309 (USA). Further examples can be found in WO 93/19335, WO 98/50752, WO 98/55221, EP 190 435 A1, EP 201 614 B1, EP 270 050 A1, EP 401 580 B1, EP 454 179 A1, EP 516 087 B1, CH 547 120, US 3,664,095, US 4,710,326, also with flat and parallel arranged individual elements. It is also possible to use spirally wound arrangements, some of which are not designed in a cross-channel structure but rather parallel to the column axis, as described, for example, in EP 068 862. The distributor packs can likewise be produced in the form of lattice structures, as described, for example, in EP 418 338 B1. Another possibility is offered by geometries with rectangular cross sections, as are customary in catalyst monoliths and are described, for example, in EP 606 964 A1. These are also designed parallel to the column axis.

There are also no restrictions with regard to the geometry of the packing elements in the case of distributor layers 8. As with the distributor packs, the decisive factor is mainly their volume-specific surface.

The liquid-distributing effect of these distributor packs and distributor layers is based on the accumulation or preferably flooding of liquid. While the remaining column packings or packing are still operated in the area of a film flow, a flood condition is formed due to the smaller hydraulic diameter of the thin distributor packs 7 and distributor layers 8 when the mode of operation is flooded. The liquid can spread over the column cross section due to the perforations in the distributor packs 7 and in the distributor layers 8, similar to the principle of communicating tubes, and flow down evenly at the lower end.

The best distribution effect is achieved when the distributor packs 7 and distributor layers 8 are operated in the flooded state. The resulting pressure loss of approximately 1 to 5 mbar per liquid distributor, however, restricts the setting of the flood condition to applications with normal pressure, positive pressure or moderate vacuum above approximately 20 mbar operating pressure. Surprisingly, however, tests have shown that a smaller distribution effect, which is sufficient for technical use, especially for intermediate distributors, is also achieved in the accumulation area. In this area, the pressure loss at approximately 0.2 to 1 mbar per distributor is significantly lower and thus opens up application possibilities even at low operating pressures.

While conventional liquid collectors and redistributors make no direct contribution to the mass transfer, the accumulating effect of the distributor packs 7 and distributor layers 8 additionally increases the separation performance. Combinations of alternately thin packing layers with a small hydraulic diameter and conventional packing layers were examined in a diploma thesis by B. Kaibel in 1999 at the Institute for Thermal Process Engineering at the University of Karlsruhe by B. Kaibel. Combinations of alternately thin packing layers with a small hydraulic diameter and conventional packing layers were investigated Accumulation of the liquid in the thin pack layers increases the separation performance in relation to the height by up to 50%. However, in this work there is no information about a liquid distributing effect of the thin pack layers.

Packing arrangements with variable geometry have been described several times, but with a different purpose. There are no indications of a liquid-distributing effect. On the contrary, the goal when using packs with variable-height geometry is that Avoiding flood conditions, especially in the lower area of the pack layers. This should enable higher gas and liquid throughputs.

In EP 858 830 A1 an attempt is made to increase the distance between adjacent packing elements at the lower edge of the packing layers by reducing the kink height there. Another possibility is to remove part or all of the material at the lower end of the packing layers, for example every second packing element. These measures serve to prevent the build-up of liquid at the lower end of the pack layers. There is no liquid-distributing effect.

WO 97/16247 describes a measure in which the geometry of the cross-channel structure is changed. The creases are no longer straight, as is customary, but are S-shaped and are arranged in such a way that the creasing direction at the lower and upper ends of the pack layers is approximately vertical. This measure is also intended to prevent the liquid from accumulating and does not lead to a liquid-distributing effect.

DE 3 918 483 C2 describes a package with a height-variable geometry in which the kinks of the cross-channel structure run vertically at the lower end. Here too, a build-up of liquid should be prevented. There is no liquid-distributing effect.

DE 2 921 270 C2 describes a pack with a cross-channel structure in which the kinks have an arcuate course. A targeted flood condition with a liquid-distributing effect cannot be set.

The desired state of flooding in the lower part of the distributor packing 7 can, however, be achieved by rearranging the individual sheet metal elements, as are basically described in DE 2 921 270 C2. The individual sheets are mounted as shown in Figure 4 so that the greatest flow resistance occurs at the lower end. In addition, the individual sheets are perforated at least in the partial area with the greater flow resistance in order to support the transverse liquid distribution in the flooded state. Prefers the distributor packs 7 are perforated in the partial area without greater flow resistance. The proportion of perforations in the total area in this area should be about 2 to 80%, preferably 10 to 30%. The transverse liquid distribution is thus further supported, since the entire area of the distributor packing 7, in which a bubble state is formed, enables a transverse liquid exchange.

As an alternative to the continuously curved kink curves, a geometry is also possible in which the kink curve at the lower end of the distributor packing 7 is inclined more towards the horizontal than at its upper end (Fig. 5). In this case too, the distributor packs 7 are preferably provided with perforations, as in the case of the distributor packs with an arched bend profile.

Alternatively, it is also possible to use the thin distributor packs 7 or distributor layers 8 alone and to create a space 10 above, in which a transverse exchange of the liquid can occur. The bubbling liquid can freely distribute above the thin distributor packs 7 or distributor layers 8. Figure 6 shows a possibility for a design with a support ring 1 1 and a support grid 12. However, any other design of spacers can be used, which allow a cross exchange of the liquid.

Instead of the preferred thin distributor packs 7 or distributor layers 8, other devices can also be used, which have an increased flow resistance compared to the packings used and trigger a bubble state (Fig. 7). For example, it is possible to use one or, preferably, several layers of wire mesh or knitted wire or wound packages. Another option is to use perforated floors or open-pore foam structures such as monoliths. These measures can also be combined in any way, for example by using arrangements of knitted wire or fillers or foam structures on perforated bases. However, the possible operating range with regard to the throughput of gas and liquid proves to be narrow.

During the experimental review, it was found that the ordered packings with a narrowed cross-section as distributor packs 7 have a particularly wide and stable operating range. This justifies their more complex design with the higher manufacturing costs. If the operating range does not vary greatly in terms of throughput, solutions adapted to the respective separation problem, such as wire networks, can also be used. In order to achieve reliable operation even under fluctuating load conditions, the use of orderly packings with a narrow cross-section is recommended.

The distributor packs 7 and the distributor layers 8 with a smaller hydraulic diameter or the modified distributor packs, which trigger accumulation only at their lower end, can be used not only with packed columns but also with packed columns in the function of liquid distributors. However, it is necessary to install these packing layers exactly horizontally. This can best be ensured by a support ring 11, as is customary in the case of tray columns for supporting the trays, in conjunction with a support grid 12.

The height of the distributor packs 7 or distributor layers 8 should be at least 0.02 m, more preferably 0.03 to 0.05 m, even in the case of small column diameters of less than 0.8 m. These values should be increased for larger column diameters. It is recommended that the height H of the manifold packs or manifold layers be preferred according to the relationship

H = 0.02 m + 0.01 * D

to choose, where D means the diameter of the column. If high demands are placed on the distribution quality, it is recommended to double these values. It is also possible to arrange two or more distributor packs 7 directly one above the other in order to improve the distribution quality (Fig. 8).

To choose the size of the distributor packs 7 or distributor layers 8, one can fall back on the usual specialist literature, especially also company documents, comparable to the choice of the mass transfer packs 6 or the full-body fill 9. If the distributor packs 7 and the distributor layers 8 are to be operated in the flooded state, this is considered to be rough As a rule, the volume-related surface area of the distributor packs and distributor layers should be selected to be approximately twice as large as the mass transfer packs 6 and the full-body fill 9. This is based on the rule that the separating internals are usually designed for approximately 70 to 80% of the flood load. Since the gas loading factor or F-factor - expressed in the form of gas velocity x gas density ^0.5 - is proportional to the hydraulic diameter ^0.5 at the flood point, it follows immediately that when the specific surface area is doubled, the flood state is reached. The hydraulic diameter of packings and packing is set to 4 / specific surface. For example, for a distillation pack 6 with a specific surface area of 250 m ² / m ^3, a suitable distributor pack 7 with 500 m ² / m ³ results.

The kink angle that the kinks form in the distributor packs 7 can be approximately 60 ° to 90 °, as in the case of the common distillation packs in a cross-channel structure. However, larger or smaller angles can also be realized.

In order to avoid unnecessary detachment of fine droplets, the kinks are preferably not rounded, but rounded, the bending radius being about 10 to 20% of the kink width.

The inclination of the kinks against the horizontal can be approximately 30 ° to 60 °. Values of 45 ° are preferred.

Adjacent pack layers 6 and distributor packs 7 are preferably rotated by 90 ° to one another. When the packing layers are installed, the layers are preferably additionally weighted dynamically (for example by tapping) or statically (for example by applying weights) in such a way that the number of contact points increases. The strength of these measures depends on the packaging material used and is known to the person skilled in the art.

The distributor packs and distributor layers can optionally be combined with conventional pre-distributors of simple design. Here the pre-distributors, for example nozzles, cause a large-scale, rough distribution of the liquid. The fine distribution is carried out in the distributor packs or distributor layers underneath.

The invention further comprises a method for operating a column equipped with distributor packs 7 or distributor layers 8, in which the gas loading, the liquid loading or the gas loading and the liquid loading are adjusted in such a way that a flooding condition occurs in the distributor packing 7 and the distributor layers 8 or in applications with low pressure loss, at least liquid accumulation occurs. In a further process, two-phase liquid mixtures are distributed without an upstream phase separation.

Claims

EXPECTATIONS 1. Liquid distributor for packed and / or packed columns with individual, in particular horizontal, layers involved in the heat and / or mass transfer, characterized in that at least one layer (7, 8) of the column for greater density and thus for a build-up, in particular flooding and for a distribution of the liquid has a specific surface that is larger by a factor of 1.5 to 10, preferably by a factor of 2 to 3 than the surface of the layer above and below. 2. Liquid distributor according to claim 1, characterized in that the height of the distributor layer, in particular the packing layer, is approximately 0.01 to 0.2 m, in particular 0.02 to 0.04 m. 3. Liquid distributor according to claim 1 or 2, characterized in that the distribution layer in particular the packing layer has perforations in the form of in particular circular holes, the proportion of perforations in the total area being about 2 to 80%, preferably 10 to 30%. 4. Liquid distributor according to claim 3, characterized in that the area proportion of the perforations is different over the pack height and preferably the area proportion of the perforations decreases from the lower to the upper pack edge. 5. Liquid distributor according to one of the preceding claims, characterized in that the distributor layer, in particular the distributor pack, is preferably embodied in a cross-channel structure, consisting of a multiplicity of bands with their side faces abutting one another, which are provided with ribs lying transversely to the longitudinal direction, the bands being arranged in this way that the ribs of strips touching each other cross each other and are made with a height of 0.01 to 0.2 m, preferably 0.02 to 0.05 m and one by a factor of 1.5 to 10, preferably by a factor of 2 to 3, have a larger volume-specific surface area than the layers or packs arranged above and below. 6. Liquid distributor according to one of the preceding claims, characterized in that above the distributor layer by spacing elements there is an approximately 0.01 to 0.2 m high, preferably 0.02 to 0.04 m high free space in which there is a cross exchange of the liquid established. 7. Liquid distributor according to one of the preceding claims, characterized in that the orderly packing of the distributor layer is carried out in a cross-channel structure, consisting of a plurality of belts which lie against one another with their side faces and are provided with ribs lying transversely to the longitudinal direction, the belts being arranged in such a way that that the ribs of strips touching one another cross and run in arcs that are parallel to one another, the arches preferably having an arc-shaped course and the ribs at the lower edge of the pack at an angle of 10 ° to 40 °, preferably 20 ° to 30 °, have against the horizontal and have an angle of 45 ° to 88 °, preferably 50 ° to 65 ° at the upper edge and this inclination points either in the same or the opposite direction as at the upper end of the package and the height of the package layer 0, 05 to 0.5, preferably 0.1 to 0.2 m. 8. Liquid distributor according to claim 7, characterized in that the preferably circular course is approximated by several straight lines, and the course at the lower end of the packing layer is inclined more weakly against the horizontal than at the upper end of the packing layer. 9. Liquid distributor according to one of claims 6 to 8, characterized in that the kink angle, which the kinks form in packs with a narrowed cross-section, amount to approximately 60 ° to 90 ° and the kinks are preferably not sharp-edged, but rounded, with the Bending radius is about 10 to 20% of the buckling width. 10. Liquid distributor according to one of the preceding claims, characterized in that the accumulation and flooding takes place in the region of the distribution device by means of narrow flow cross sections which have an increased flow resistance in comparison to the packings or packing elements used and instead of or in addition to the perforated plates, one or preferably several Layers of wire nets or wire mesh, packings wound from sheet or fabric sheets, open-pore foam structures such as monoliths used. 11. The method for operating a contact apparatus equipped with distributor packs or distributor layers according to one of the preceding claims, characterized in that the gas load, the liquid load or the gas load and the liquid load are adjusted together in such a way that a flood condition occurs in the distributor packs and the distributor layers or in applications with low pressure loss, at least liquid accumulation occurs. 12. The method according to claim 11, characterized in that a two-phase liquid mixture is distributed and the liquid distribution is carried out without an upstream phase separation in a separation vessel. 13. The method according to claim 11 or 12, for operating a fixed bed reactor with counterflow of gas and liquid, characterized in that distributor packs or distributor layers are used for distributing the liquid at the upper end of the catalyst bed and optionally within the catalyst bed, the hydraulic diameter being chosen so is that in the selected operating state the flood condition occurs in the distribution packs or distribution layers.